Permeation of supercritical fluids through a MFI zeolite membrane

This work involves the joining of two new technologies: supercritical fluids (SCF) and inorganic microporous materials. The objective of this study is the determination and description of transfer mechanisms of supercritical fluids through inorganic microporous membranes whose selective layer is constituted of MFI zeolite, a material with particular properties of porosity, crystalline structure and adsorption. To describe the evolution that experiences the supercritical fluid inside the microporous medium as a function of pressure and temperature, models based on the formulation of Stefan-Maxwell and ordinarily used for gas phase transfer were selected. A statistical analysis of permeation data allow to distinguish between the convective (or Poiseuille viscous) and diffusive (Knudsen flow) contributions, as well as to highlight the effect of adsorption at wall. As a whole it appears that the transfer of SCF results from a combination of diffusive mechanism and interaction with the membrane surface, well in agreement with what the proximity of sizes of pores and gas molecules enables to foresee. Under the assumption that adsorption is characterised by a low occupation rate of available places inside the micropores, the Stefan-Maxwell equations give a good description of the general system behavior. (C) 2001 Elsevier Science Ltd. All rights reserved.